Internal combustion engines for automobiles in recent years tend to include variable valve mechanisms capable of changing valve timing or valve lift amounts at intake valves or exhaust valves. The variable valve mechanism has improved in technology in terms of increasing the degree of control freedom, enlarging the operational range, and improving response. More specifically, variable valve mechanisms capable of continuously and variably controlling the valve lift amount have been developed. The amount of air taken into cylinders by the lift continuous variable valve mechanism is controlled by intake valves instead of a throttle valve. This control realizes reduction in pump loss and a Miller cycle, and improves fuel consumption of an internal combustion engine. Turbo-downsizing internal combustion engines that improve the fuel consumption by mounting a turbocharger, and improve the mean effective pressure by reducing the cylinder capacity have been developed.
A control device of an internal combustion engine mounted with such a variable valve mechanism or a turbocharger detects or estimates an amount of intake air flowing through an intake pipe using an air flow sensor or a pressure sensor provided at the intake pipe. A charging efficiency is calculated from the value. An amount of ignition control is calculated on the basis of the charging efficiency and a rotation speed.
Patent Document 1 discloses a technique of correcting the ignition timing retard for preventing a transient knock during acceleration in consideration of an operational state of an engine. In the technique disclosed in Patent Document 1, an intake air temperature level of the engine before acceleration is estimated on the basis of determination criteria, such as whether the state is idle or not and whether the water temperature level is in a warm-up state or not, and changes the transient retard correction amount in response to the estimated temperature level. Further in the technique, the transient retard correction amount at a low vehicle velocity or a low rotation speed is increased, thereby preventing transient knock that tends to occur at a low velocity.
Patent Document 2 discloses a technique of controlling an internal combustion engine mounted with a turbocharger that estimates the intake air temperature during operation moment by moment and controls the ignition timing and air-fuel ratio in response to the estimated intake air temperature. The technique disclosed in Patent Document 2 includes computation means for acquiring the intake air efficiency coefficient and temperature correction coefficient specific to an engine and uniquely determining the intake air temperature by means of a linear function having parameters of the coefficients specific to the engine and a ratio of a mass of air per unit cycle to an intake pipe pressure. The ignition timing is corrected to retard side and the air-fuel ratio is corrected to the rich side, with increase in intake air temperature estimated by the computation means.    Patent Document 1: JP Patent Publication (Kokai) No. 7-180643 A (1995)    Patent Document 2: JP Patent Publication (Kokai) No. 6-33819 A (1994)